Grinding wheel



Sept. 7, 1937. A. 'r. SOHLSTROM 2,092,591

GRINDING WHEEL Filed Aug. 17, 1955 F/G. Z

I [Ill/1111M awe/W000 ALBERT T SnHLsTRaM Patented Sept. 7, 1937 UNlTED STATES} PATENT OFFICE 2,092,591 GRINDING WHEEL Application August 17, 1935, Serial No. 36,637

6 Claims. (01. 51-206.)

The invention relates to grinding wheels, and with regard to its more specific features to Wheels having a non-grinding center. One object of the invention is to provide a wheel structure sus- 5 ceptible of embodiment in a comparatively thin disk of relatively large diameter. Another object of the'invention is to provide a strong construction for diamond cut-off wheels and the like. Another object of the invention is integrally to unite a metal disk center with an annular diamond abrading portion. Another object of the invention is to provide a simple and practical method for the construction of a diamond cut-off wheel. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and the several steps and relation and order of each of said steps toone or more of the others thereof, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims. I

In the accompanying drawing, in which are shown three of many possible embodiments of the mechanical features of this invention,

Fig. l is a greatly enlarged fragmentary radial cross sectional view of a wheel constructed according to the invention,

compositions, such as resinoids of the phenol formaldehyde type. Apparatus ofthis general class is shown in the patent to Sanford No.

1,981,970. Referring now to Fig. 1, I provide a pair of aluminum disks l0. Only a fragment of the disks I0, I is shown in Fig. 1; theymay be of the orderof .013" in thickness and in diameter and preferably there is a central hole through each of them in order that the completed wheel may be mounted upon an arbor.

Having provided a circular mold, a central core fitting the holes in the disks, a pair of annular disk mold members of the same area as the 50 aluminum disks l0, and a pair of outer annular mold members whose area is'identical with the area of the outer grinding portion to be formed, I place one of each of such mold members on the lower platen of a heat and pressure molding apparatus, inside the usual retaining ring. I now Fig. .2 is a view similar to Fig. 1, showing in place one of the aluminum disks l0 over the central core and upon the lower-mold member which matches it. There is an annular space outside of the aluminum disk l0 and this I fill. to an appropriate depth with a mixture of resinoid binder and abrasive grit. While so far as certain constructional features are concerned, this abrasive grit might be any desired or known abrasive,

such as aluminum oxide or silicon carbide, the

construction lends itself particularly to the manufacture of a diamond abrasive wheel and I prefer to use a diamond grit, such as is known commercially as bort, or I may use in some cases boron carbide (34C) grit.

I now sprinkle a layer of resinoid powder upon the disk l0. Having thus deposited in the mold a quantity of resinoid l I having dispersed therein diamond particles l2, and having filled the outer annular part of the mold so that the mixture is level with the lower aluminum disk I0, I place a disk 13 of cloth upon the disk l0 andmaterlal H and, l2 covering the entire area thereof. I next sprinkle another layer of resinoid powder upon the upper side of the cloth I3. I now place the second disk l0 upon the cloth l3. Next I place in the outer part of the mold, and above the cloth l3, a quantity of resinoid powder or grain with diamonds. l2 dispersed therein equal to the quantity under the cloth I3. I then place the mating mold pieces in position and the wheel may now be formed by the application of heat and pressure.

Fig. 1 shows the wheel in fragmentary enlarged cross section after it is made. In the formation of the wheel the abradant annulus I5 is considerably compressed, so the space in the mold for the abrasive grain and bond will be considerably thicker than the thickness of the finished abrasive annulus l5, and there should be as much space below the cloth l3 as above it. I have shown the abrasive portion [5 as somewhat thicker than the central portion including the disks l0, l0,

but the difference may be of the order of .001"

or .002" or even less. A practical Wheel may be made in which the thickness of the abrasive portion IS in the finished wheel is the radial dimension of the portion I 5 being 1", the diameter of the entire wheel 6", the thickness of the aluminum disks l0 being .013".

While I may use any type of cloth or fiber for the portion 13, I prefer to use cloth which is fairly tough but not too thick, and I also prefer to use rather open mesh cloth the pick and sley of which is on the order-of cheese cloth. I may even use leno, but I prefer to use linen with an open weave, and if a cotton cloth is used a long staple cotton should be selected.

In the setting of the wheel, after the heat and pressure are applied, the entire substance shrinks, but the coefiicient of expansion of aluminum is close enough to that of the resinoid to avoid dishing of the product. I prefer to use alu minum because excellent results lhave been achieved in practice therewith, but any metal which will contract after heating without dishing may be employed. Prior to manufacture of the wheel I preferably clean the aluminum disk l0, and this may be done with abrasive paper or cloth or the like. By removing part at least of the oxide on the surface of the aluminum and making scratches therein, the resinoid firmly adheres to the aluminum and the center |6 of the wheel is virtually an integral piece.

It will be noted that the resinoid, when set, exists in the form of an integral piece from the outside of the abrasive annulus I!) right to the central hole, but the diamond abrasive grit is located solely in the grinding portion [5. The

' resinoid is reinforced by the cloth disk 13, and

a feature of substantial importance is that flexibility and strength are imparted to the resinoid in the junction circle I! where the entire wheel is held together. In the use of thin cutting-off wheels of this type, whenever a side strain is placed upon the wheel, the juncture between the non-abrading disk andthe abrading annulus is usually the weak point and by my present invention a tough union is achieved, and one which has sufficient flexibility to bend rather than break under normal shocks.

For a somewhat thicker wheel, I may adopt the construction shown in Fig. 2. This differs from the construction shown in Fig. 1 in comprising three aluminum disks l0, l0, In, two cloth disks I3, l3 and an abrasive annulus |5a which is thicker than the annulus 15 of Fig. 1. The wheel of Fig. 2 may be made by first forming an abrasive annulus united to a pair of disks Hi, In with one disk of cloth l3 therebetween as in the case of Fig. 1, and molding under heat and pressure for a limited time, for example for about two minutes, whereby the resinoid material is not completely set. The resultant product may then be placed in another mold with the addition of a further cloth disk l3 and another aluminum disk I0 and additional resinoid and diamond mixture II, I! and a further molding operation under heat and pressure for a longer period, for example 20 minutes, will serve to unite the parts together to form an integral wheelfas shown in Fig. 2. The quantity of abrasive and bond mixture in the mold should be selected to give the desired density in the final product. It is the thickness of the mold rings themselves together with the mold limiting stops which determines the shape of the final product. For the exact ingredients which may be used for the manufacture of the wheel of this invention in a preferred form, reference may be had to the patent to Sanford hereinbefore referred to, as the material therein specified may be used in carrying out this invention. However, the proportions may be considerably varied to produce wheels of different characteristics, and furthermore, so far as the mechanical features of this invention are concerned I am not limited to bonds of artificial resinous material, but may use other bonds.

Referring now to Fig. 3, I therein illustrate an embodiment of the invention in which the central reinforcing member is a sheet I! of metal foil having holes l8 therein. This may be aluminum foil of a thickness of the order of .002" or .003". In manufacturing the wheel of Fig. 3 I follow the method already indicated for the wheel of Fig. 1, except that I use a slightly greater amount of resinoid cementing material 20 to unite the disks I 0, l0 together, with the foil l1 between them. It will be seen that the abrasive annulus l5b is likewise an integral mass as the resinoid and diamond mixture extends through the holes I8.

I have found that an artificial resinous material, such as that sold under the trade name Bakelite has, when molded under heat and pressure, a distinct adhesive power which causes it firmly to adhere to a metal surface, such as aluminum, especially if the metal surface is brightened as by the use of abrasive paper as already specified. This characteristic together with the reinforcing feature described permits the manufacture of a strong rugged wheel.

For the grinding of materials of a hardness greater than 9 on Mohs scale, or greater than 12 or 13 on Mohs scale extension, such as cemented tungsten carbides, tantalum carbide, and also boron carbide, a diamond wheel manufactured in accordance with the invention presents marked superiority. In a grinding action such as indicated, the cloth disks l3 are so soft in comparison with the abrasive and the substance being cut that they completely disappear during grinding and do not materially interfere with the grinding action. It will be noted that, according to the embodiment of the invention illustrated in Figs. 1 and 2, the abrasive grainl! is virtually forced, into the cloth I 3, so that the wheel has abrading properties along its entire peripheral width. In the case of the embodiment shown in Fig. 3, the aluminum foil H has relatively speaking about the resistanceof putty when compared to the abrasive material with which it is integrally united, and therefore it wears away without affecting the grinding actioni Nevertheless, it possesses sufficient tensile strength and elastic, qualities materially to strengthen the entire integral assembly. At all events, whatever the explanation, a wheel made with a central disk-like reinforcement, such as the cloth l3 or the aluminum foil IT, has strength greater than a wheel having no such reinforcement, and for superior results I prefer to use materials of strength and elasticity such as indicated. I might substitute a very thin section of steel for the aluminum foil II, in so much as owing to the thickness thereof and the holes provided therein, despite differences of the coefficients of expansion, it would not cause buckling of the central portion, but in actual practice I achieve superior results using aluminum.-

The heat and pressure required for setting the Bakelite will be readily understood by those skilled in the art of molding Bakelite; -I merely note that a temperature of 140 C., two tons to the square inch pressure, and a time factor of 20 minutes for complete setting of the product is satisfactory. I have not illustrated the molding parts herein for the forms of molds for the manufacture of resinoids is understood to those skilled in the art, and further more in carrying out my invention many different forms of molds may be used and I have clearly described one form and type so that the invention may be readily carried out in practice.

'therein, can be advantageously used for cutting off or slotting pieces of boron carbide, tantalum carbide, tungsten carbide, the cemented carbide bodies and other extremely hard substances.-

The invention permits the production of wheels which are extremely thin and at the same time sufficiently strong and rigid and of composite construction. The manufacture of a wheel having diamond.- abrasive which is homogeneous throughout involves the placing of diamond abrasive in a non-grinding central part which is expensive. The method of the invention, furthermore, can be carried out quite economically.

It will thus be seen that there has been provided by this invention a method and an article in which the ,various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the surrounding said disksyand a resinoid uniting said disks and said annulus, all parts being permanently and integrally united forming an integral structure thereof.

2. A grinding wheel according to claim 1 in which the resinoid between the disks is reinforced by cloth.

3. A grinding wheel according to claim 1 in which the resinoid between the disks is reinforced by metal foil.

4. A grinding wheel according to claim 1 in which the resinoid between the disks is reinforced by metal having holes therein.

5. A grinding wheel comprising a pair of metal disks, a grinding annulus surrounding said disks, and cement for said disks which extends integrally from the annulus substantially to the center of the disks, all parts being permanently and integrally united forming an integral structure thereof.

6. A method of forming a grinding wheel comprising placing a metal disk in a mold, covering it with resinous powder, filling an outer portion of the mold with abrasive grain and a resinous bond, covering the disk with a; fibrous reinforcing medium, adding more resinous powder, placing a second metal disk thereon, adding more abrasive and resinous bond, and maturing under ALBERT T. SOHLS'I'ROM. 

